The invention relates to a means for pressure and quantity control of the hydraulic drives of an injection moulding machine having the features set forth in the preamble of claim 1.
In such plastic processing machines various hydraulic drives are provided, in particular an injection cylinder for injecting the plastic into the mould and a clamping cylinder for the opening and closing movement of the displaceable mould half and these must be actuated on the one hand in accordance with a predetermined speed program and on the other must be subjected to specific pressures to hold the mould halves together, lower the pressure before closure of the mould to avoid damage to the mould should a casting not be completely ejected and to generate a predetermined after pressure in the injection cylinder after insertion of the plastic into the mould to keep the mould cavity filled with plastic. According to the prior art the particular displacement necessary and the desired pressure can be generated with a regulating pump, i.e. a pump with variable displacement. Combined pressure regulators and quantity regulators for such variable displacement pumps are known. The pressure regulating time depends on the relatively sluggish response behaviour of such pumps. If for example the pressure drop does not take place fast enough the injection pressure of the injection cylinder may rise to such an extent that the clamping pressure of the mould is briefly exceeded and plastic emerges.
If however the pressure is governed at a pressure vaIve connected to the pressure line of the adjusting pump an additional regulatable valve is required.
The problem underlying the invention therefore resides in simplifying the quantity or volumetric and pressure control of an injection moulding machine.